Control device for a heating element



March 1, 1960 w. BRANDL 2,927,186

CONTROL DEVICE FOR A HEATING ELEMENT Filed Nov. 4. 1958 3|- 34 l 29-1 g I g a l L-..

3 VVJi/VV United sta fis Patfint CONTROL DEVICE FOR A HEATING Wilhelm Brand], Zurich, Switzerland i Application November 4, 1958, Serial No. 771,858

Claims priority, application Switzerland November 4, 1957 3 Claims. Cl. 219-20 The present invention relates to a control device for a heating element such as is known for example from the US. Patent No. 2,850,611. This control device is provided with a pressure-sensitive switching element which through the agency of an adjustable switch blade, controls a switch for supplying current to the heating element, with which the said switching element is connected by way of a pipe.

The control device according to the invention is characterized in that there is superimposed on the switch blade a compensating spring whose action, in accordance with the setting of the switch blade, is such that if the switch fails the switch blade closes the contacts of a short-circuiting cutout safety arrangement after a pressure increase in the heating element independent of the adjusted temperature.

One example of embodiment of the subject of the invention is illustrated in the accompanying drawing. The heating element to which the control device is connected, is illustrated diagrammatically and on a relatively small scale.

The control device 1 comprises a carrier plate 2 on which a pressure-sensitive element is arranged. In the illustrated example of embodiment this pressure-sensitive element consists of a bellows 3, whose base is fixedly secured to a strap 4 mounted on the carrier plate 2. The movable end of the bellows 3 is connected to an elastic switch blade 7 by means of a rod 5 and nuts 6. This switch blade 7 extends through a bearing member 8 which is fixed on the carrier plate 2. Extending perpendicular to this bearing member 8 is a second bearing member 9 in which an adjusting screw 10 is mounted. This screw 10 comprises a knob 11, having a pointed portion 12 which is movable opposite a scale 13. Provided at the end of the bearing member 9 is a further screw 14, by means of which the initial stress of the switch blade 7 can be regulated. Adjusting nuts 15 serve to maintain the desired amount of initial stress. Provided between the switch blade 7 and the screw 10 is a compensating spring 16 which extends from the lower end of the switch blade 7 to the point of the screw 10 parallel to the switch blade 7, and then extends at an angle to the latter by way of a slot in the bent-over end 17 of the bearing member 9. The end 18 of the compensating spring 16 is situated over the head 19 of a bolt 20 which is fixed on the end of the switch blade 7. The free end of this bolt 20 operates the press-button 21 of a microswitch 22, which is fixed by means of screws 23 to the carrier plate 2. This end also carries a contact 25 which co-operates with a fixed, adjustable contact 24 arranged on the carrier plate 2.

The bellows 3 is connected through a pipe 26 (or a flexible tube) to the evacuated vessel 27 of a heating element 28, which serves for heating a device 29 (e.g. a cooking pot or a washing machine tube). The vessel 27 contains a heating medium which is heated by means of an electrical resistance 30. This heating resistance 30 is connected by way of a conductor 31 to the switch 2,927,186 7 Patented Mar. 1960 22 and by way of a conductor 32 to one phase of the current source 33, the other phase being connected by way of a conductor 34 to the other contact of the switch 22. The contacts 24, 25 also serve as short-circuiting cutout means to guard against failure of the switch 22 to operate, since they are connected through the conductors 35 and 36 to the conductors 31 and 32 respectively.

The control device which has been described hereinbefore operates in the following manner:

The desired heating temperature is adjusted by means of the knob 11. The bolt 20 is thereby pressed against the press-button 21 and the circuit of the heating resistance 30 is closed. The movement of the screw 10 lifts away the end 18 of the compensating spring 16, so

i that it does not operate on the bolt 20. When the set temperature is reached, the pressure in the vessel 27 rises, and the bellows 3 switches off theheating resistance 30 by way of the switch blade 7, the bolt20, and the switch 22. If the switch 22 fails and remains'conuectedup, the contacts 24, 25 short-circuit the heating resistance 30. If no compensating spring 16 were provided, the control travel of the contact 25, i.e. the pressure increase which can take place before short-circuiting, would be dependent on the adjusted temperature. Thanks to the compensating spring 16 this can be avoided, so that for a specific pressure or temperature increase above the adjusted value, closing of the contacts 24, 25 will always be guaranteed independently of the amount of this adjusted value. Depending on the adjustment of the screw 10, the end 18 of the compensating spring 16 is spaced more or less far from the head 19 of the bolt 20. If the pressure in the bellows 3 rises above the adjusted value, it must act in opposition not only to the effect of the elastic switch blade 7 but also to the action of the compensating spring 16. Thus the pressure increase above the adjusted value which will bring about short-circuiting can be kept constant.

To sum up, therefore, the control device which is illustrated in the drawing is characterized in that a compensating spring is so mounted, that, irrespective of what pressure is adjusted, after switching-0E a constant excess pressure is always necessary in order to lift away the elastic switch blade so far that it operates a short-circuiting cutout means or a circuit breaker switch, and also prevents the pressure-sensitive element from expanding more than is necessary when the control device is relieved of load.

In other words, the compensating spring acts to prevent the contacts 24 and 25 from closing the short-circuiting circuit for the heating resistance 30 until a definite pressure, in addition to that required to release the microswitch, is established in the bellows 3. Thus, if the pressure in the bellows 3 is suflicient to cause the adjusted switch blade 7 and the bolt 20 to release the press button 21 and the microswitch opens, then the heating resistance cools at once. No additional pressure reaches the bellows 3. The contacts 24 and 25 are then not closed. If, on the other hand, the microswitch fails to open, the resistance 30 continues to build up pressure in the bellows, the switch blade moves the bolt into contact with the compensating spring 16 and against its pressure, and the contacts 24 and 25 are brought together closing the short-circuiting circuit. The heating resistance 30 is thus de-energized, and a dangerous condition is avoided.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

7 3 What I claim is:

1. A control device for an'electrical heater containing a fluid expansible with heat, comprising a bellows connected to the fluid in the heater responsive to the pressure-thereof, an adjustable switch blade having one end restrained and connected to said bellows for movement thereby, a boltconnected to the free endof said switch blade for axial movement to close the heating circuit through the electrical heater, a short-circuiting circuit for the electrical heater including two normally open contacts, one of such contacts being carried by said belt for closing said contacts following movement away from heating circuit closing position, and a compensating spring having an end adjacent the end of said bolt opposite to that which acts to close :the heating circuit for retar inglos ng f said .shorecircuiting uit conta ts until a pr d term n d pressure exists in said b l above that for which said switch ,blade is adjusted.

v2. A control devicc accordingrtoclaim 1, wherein said comp ting pr ng i djustabl with s id. r-s itch blade- 3. A control device for an electrical heater comprising a heating vessel, an electrical resistance ,for heating said vessel, a microswitch for opening and closing the circuit through said electrical resistance, a bellows connected to at said vessel for expansion and contraction responsive to the pressure therein, an adjustableswitch blade operable by said bellows, a bolt carried by said switch blade for movement with said switch blade to close said microswitch, and in opposite direction to permit said microswitch to open an electrical circuit short-circuiting said electrical resistance, andnormally open contacts for said short-circuiting circuit, one of said contacts being carried on said bolt "for closing said contacts when said bolt is moved to permit said microswitch to open, in combination with a compensating spring superimposed on said switch blade and spaced from the head of said bolt in the adjusted position of said switch blade to apply pressure to said bolt head when pressure in said bellows rises above adjusted value, whereby said normally open contacts are closed at -a predetermined pressure increase above the adjusted value.

References Cited in the filc'of this patent UNITED STATES PATENTS Fry May 11, 1954 

